This application is based upon and claims benefit of priority of Japanese Patent Application No. 2000-255908 filed on Aug. 25, 2000, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a pressure sensor having a semiconductor sensor chip, such as an oil pressure sensor for use in an automotive vehicle.
2. Description of Related Art
An example of a pressure sensor of this kind is disclosed in JP-A-7-243926. In this pressure sensor, a semiconductor sensor chip is mounted via a substrate on a depressed portion formed in a case. The depressed portion is filled with oil to cover the sensor chip, and the oil is hermetically covered with a metallic seal diaphragm. A pressure to be measured is imposed on a front surface of the seal diaphragm, and the imposed pressure is transferred to the semiconductor chip via the oil covering the semiconductor sensor chip. That is, the pressure to be measured by the semiconductor chip is imposed thereon from the front surface of the seal diaphragm which is opposite to the substrate of the sensor chip. This type of the pressure sensor is called a front-surface-type pressure sensor.
A pressure sensor in which the pressure to be measured is imposed on the rear surface of the sensor chip (a rear-surface-type pressure sensor) is also required to meet a certain pressure-sensing arrangement. A rear-surface-type pressure sensor made by the inventors as a proto-type is shown in FIG. 5. FIG. 5 briefly shows the front surface side of the sensor chip. A sensor chip J2 is mounted in a depressed portion J4 formed on one end surface J3 of a sensor case J1. Four terminals J5 for connecting the sensor ship J2 to an outside circuit are disposed around the depressed portion J4. The terminals J5 are molded in the sensor case J1 so that they extend in a longitudinal direction of the sensor case from one end surface of the sensor case (the front surface side) toward the other end surface.
The sensor chip J2 is a semiconductor sensor chip having a diaphragm and is pasted on the bottom surface of the depressed portion J4 via a sensor chip substrate. A through-hole J6 is formed in the sensor case J1, so that a pressure to be measured is imposed on the sensor chip diaphragm through the through-hole J6. The sensor chip J2 is disposed in the depressed portion J4 to hermetically close the front side opening of the through-hole J6. The rear-surface-type pressure sensor that senses a pressure supplied from the rear surface of the sensor chip is made in this manner. Further, the front surface of the sensor chip may be covered with oil and a seal diaphragm in the same manner as in the pressure sensor disclosed in aforementioned JP-A-7-243926, and another pressure may be supplied to the front surface of the sensor chip from the seal diaphragm side. In this manner, a pressure difference between the pressure supplied to the rear surface and the pressure supplied to the front surface may be detected by the sensor chip.
In the pressure sensor structure shown in FIG. 5, it is necessary to hermetically seal a boundary of the sensor chip J2 and the opening of the through-hole J6 to avoid pressure leakage through the boundary. For this purpose, it is effective to fill a space J7 between the sensor chip J2 and inner walls of the depressed portion J4 with a sealing material such as resin. However, the space J7 has to be sufficiently large to effectively fill the space J7 with a viscous sealing material. The depressed portion J4 could be enlarged as shown with a dotted line in FIG. 5. However, if the depressed portion J4 is enlarged, the terminals J5 must be moved further outside. This causes a problem that an entire size of the sensor case J1 has to be made large.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved pressure sensor, in which a pressure to be measured is supplied to a rear surface of a sensor chip through a through-hole formed in a sensor case, and a sensor chip is hermetically connected to the through-hole without enlarging the pressure sensor size. Another object of the present invention is to provide a compact pressure sensor that detects a pressure difference between pressures applied to both surfaces of the sensor chip.
The pressure sensor is composed of a cylindrical sensor case and a housing, both connected to each other by calking one end of the housing. A depressed portion is formed on one longitudinal end surface of the sensor case, where the sensor case is coupled with the housing. A semiconductor sensor chip having a front surface and a rear surface is mounted in the depressed portion so that the front surface faces the housing. A first pressure is imposed on the rear surface of the sensor chip through a through-hole formed in the sensor case. A second pressure introduced from the housing is imposed on the front surface of the sensor chip via oil confined to cover the front surface. The sensor chip detects a pressure difference between the first and the second pressures and converts the detected pressure difference into an electric signal.
The sensor chip has to be hermetically mounted in the depressed portion so that the first pressure does not leak to the second pressure side. For this purpose, a sealing material is charged into a space between a sidewall of the depressed portion and a side periphery of the sensor chip. Plural holes for charging the sealing material are formed around the depressed portion. The charging holes are positioned between terminals electrically connecting the sensor chip to an outside circuit. In this manner, the charging holes are formed without enlarging the sensor case size.
Preferably, the depressed portion is formed in a rectangular shape, and the charging holes are formed at four corners of the rectangular depressed portion. In this manner, the sealing material is uniformly and smoothly charged in the charging space. The sensor chip is hermetically mounted on the sensor case to prevent the first pressure leakage to the second pressure side. Further, a tapered slope outwardly enlarging the charging hole is added to the charging hole. The sealing material further smoothly flows along the tapered slope into the charging space.
Alternatively, the sensor chip may detect only the first pressure imposed on the rear surface thereof by eliminating the second pressure supply from the housing side. In this case, the pressure sensor functions as an absolute pressure sensor.
According to the present invention, the sensor chip is hermetically mounted on the sensor case without enlarging the size of the pressure sensor.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.